• 한국전기전자재료학회논문지
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• 제23권11호
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• pp.854-858
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• 2010

In this study, we have investigated the effects of Cr dopant on the sintering and electrical properties of ZnO-$Sb_2O_3$ (ZS) ceramics for varistor application. Spinel phases including $\alpha-$ and $\beta$-type was formed at ZS system and $\alpha$-spinel was stabilized by Cr doping in ZS system. Densification of ZS and ZSCr system was retarded to $1000^{\circ}C$ by the formation of spinel at $800^{\circ}C$. The morphology and its distribution of spinel phases in ZS system was homogeneous but disturbed by Cr doping. In ZSCr the densification of ZnO compared with ZS system was more retarded by low concentration of Zn interstitial defects induced by Cr doping in addition to the effect of spinel phase formation. The defects in each system were identified as attractive coulombic center (ZS: 0.13 eV, ZSCr: 0.12 eV) and singly charged oxygen vacancy $V_0^{\cdot}$ (ZSCr: 0.33 eV). In all ZS and ZSCr system have week varistor behavior by the formation of double Schottky barrier at grain boundary but its stability of barrier was very sensitive to sintering temperature.

• 한국보건간호학회지
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• 제14권1호
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• pp.26-40
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• 2000

This study was conducted to find out residential environment, mood states, ADL(Activity Daily Living) and nursing need of the elderly who live alone. The questionnaire survey was conducted on 154 single household elderly over 65years who live n D-city, Kangwon Province. The data were collected between September 1. 1999 and October 17, 1999 and analyzed by means of SPSS package. The results were as follows; 1. The percentage of the subjects who owned their house was no were than $13\%$., which showed that they still belonged to the economically vulnerable class. As for their residential environment, the average indoor temperature and humidity level were $16.45^{\circ}C\;and\;44.62\%$ respectively during the daytime between September and October, which proved to range within the standard scope. The average indoor illumination level was, however, 43.61 Lux, which showed that their illumination environment was very poor. 2. The average score of their mood states was 3.31. which turned out to be rather low. 3. The mean score of ADL was 1.69, which showed that they didn't have any serious inconveniences in their ordinary lives. 4. The mean score of their nursing need was 275, which proved to be close to the normal level. 5. The higher the room humidity was, the higher their nursing need increased. The higher the degree of illumination level was, the lower the degree of their nursing need was and the higher the level of ADL was. 6. The major factors influencing their moon status were the frequency of their contact with children and room humidity. These two factors could account for $22\%$ of the total mood status. These results suggest that the residential environment should be necessarily considered in the psychological nursing intervention for the elderly who live alone and they should be urgently supported in terms of health policy so that they can maintain the optimum level of illumination during the daytime.

• 한국지구과학회지
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• 제24권6호
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• pp.533-548
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• 2003

지표 및 연직기상자료를 이용하여 포항지역 주변의 겨울철 탁월풍 현상을 살펴보고 이 현상을 분석하기 위해 RAMS를 이용한 수치모의를 수행하였다. 조사결과, 상층대기에서는 서풍을 보였으나 지표부근에서는 남서풍이 탁월하였다. RAMS를 이용하여 겨울철 풍계를 살펴본 결과, 이러한 겨울철 탁월풍 현상은 해안선의 형태와 낮은 구릉지, 그리고 바다와 육지의 분포 등의 지형적 특징에 의해 크게 영향을 받는 것으로 분석되었다. 이상의 모형결과의 정확성을 살펴보기 위해 일 중 지속적인 남서풍이 관측되었던 날들의 풍속, 기온, 풍향을 대상으로 관측값과 모형결과값을 비교하였다. 일반적으로 기상관측망은 공간적으로 조밀하지 못하기 때문에 국지순환계의 특징을 자세히 살펴보기가 쉽지 않다. 하지만 이러한 공간적 고분해능을 만족하는 수치모형을 이용한다면 더욱 정확한 결과를 제공받을 수 있을 것이다.

• Transactions on Electrical and Electronic Materials
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• 제17권5호
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• pp.261-269
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• 2016

A high-performance transmit/receive (T/R) switch is essential for every radio-frequency (RF) device. This paper proposes a T/R switch that is designed in the CEDEC 0.13 μm complementary metal-oxide-semiconductor (CMOS) technology for 2.4 GHz ISM-band RF applications. The switch exhibits a 1 dB insertion loss, a 28.6 dB isolation, and a 35.8 dBm power-handling capacity in the transmit mode; meanwhile, for the 1.8 V/0 V control voltages, a 1.1 dB insertion loss and a 19.4 dB isolation were exhibited with an extremely-low power dissipation of 377.14 μW in the receive mode. Besides, the variations of the insertion loss and the isolation of the switch for a temperature change from - 25℃ to 125℃ are 0.019 dB and 0.095 dB, respectively. To obtain a lucrative performance, an active inductor-based resonant circuit, body floating, a transistor W/L optimization, and an isolated CMOS structure were adopted for the switch design. Further, due to the avoidance of bulky inductors and capacitors, a very small chip size of 0.0207 mm² that is the lowest-ever reported chip area for this frequency band was achieved.

• 대기
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• 제21권4호
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• pp.447-454
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• 2011

As dust storms originated in Neimongu Plateau and Manchuria became more frequent in Korea, there was a growing need for Asian Dust (Hwangsa) monitoring stations in North Korea, which is a pathway of Asian Dust to South Korea. The South Korean and the North Korean Governments agreed to build the Automatic Weather System and the PM10 measurement instruments in the Gaeseong Industrial Zone and the Keumgangsan Tourist Region, North Korea in 2007. PM10 mass concentration data in the Keumgangsan Tourist Region could be collected only during the period from September 2007 to May 2008. In this study, daily, monthly and diurnal variations of PM10 mass concentration of the Keumgangsan are analyzed and compared with those of Sokcho and Gwangdeoksan. Three sites show similar variations in daily and monthly means. Correlation coefficients (r) between Sokcho and Keumgangsan, and between Gwangdeoksan and Keumgangsan are 0.89 and 0.67, respectively. But diurnal variation at Keumgangsan has a distinct feature compared to the other sites. Diurnal PM10 variation shows two peaks around 8 AM and 4-5 PM and very low at night. The difference between the daily maximum and minimum is $20{\sim}60{\mu}g\;m^{-3}$ during September to November 2007. Temperature, relative humidity and wind speed from the Keumgangsan AWS data were compared with those from the Changjon station, and showed good correlation each other except wind speed.

• 한국대기환경학회지
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• 제2권1호
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• pp.73-79
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• 1986

This study is carried out to determine the concentration of the ozone and the factors affecting the variation of ozone concentration in the ambient air in Seoul. The one-hour average concentration of ozone $(O_3)$, sulfur dioxide $(SO_2)$, nitrogen oxides (NO and $NO_2$), suspended particulate (TSP), carbon monoxide (CO) and non-methane hydrocarbon (NMHC) at 5 sites in Seoul measured from September to October in 1983 and 1984 were analysed statistically along with meteorological data for the same period. The results were as follows; 1. The average concentrations of ozone at 5 sites during the period ranged from 3.3 to 9.1 ppb, they were below 20 ppb of the ambient air quality standard of Korea. 2. The maximum hourly concentration of ozone occurred between 2 and 3 p.m. in a day and concentration at night were very low but higher concentrations were observed at around 4 a.m. 3. The concentration ratio between NO and $NO_2$ in Seoul was relatively lower than that for the cities of foreign countries reported so far. 4. The ozone concentration has negative correlationships with the concentration of other primary pollutants$(SO_2, NO, NO_2, CO and NMHC)$ in simple regression analyses. 5. The ozone concentration was positively correlated to wind speed, temperature and insolation intensity but negatively correlated to relative humidity. 6. Stepwise multiple regression analysis of the ozone concentration to the pollutants and meteorological factors indicate that insolation intensity and $[NO_2]/[NO]$ were the primary influencing factors. 7. The three factors of insolation intensity, $[NO_2]/[NO] and NO_2$ concentration had a significant combined effect on the ozone concentration $(r^2 = 0.47-0.57)$.

• 한국대기환경학회지
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• 제22권1호
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• pp.73-84
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• 2006

Hazardous Air Pollutants (HAPs) are characterized by being relatively heavier and denser than that of ambient air due to the various reasons such as higher molecular weight, low temperature and other complicated chemical transformations (Witlox, 1994). In an effort to investigate transport and diffusion from instantaneous emission of heavy gas, Lagrangian Particle Dispersion Model (LPDM) coupled with the RAMS output was employed. Both deposition process and buoyancy term were added on the atmospheric diffusion equations of LPDM, and the locations and concentrations of dense gas particle released from instantaneous single point source (emitting initially for 10 minutes only) were analyzed. The result overall shows that adding deposition process and buoyancy terms on the diffusion equation of LPDM has very small but detectable effect on the vertical and horizontal distribution of Lagrangian particles that especially transported for a fairly long traveling time. Also the slumping of dense gas can be found to be ignored horizontally compared to the advection by the horizontal wind suggesting that it was essential to couple the Lagrangian particle dispersion model coupled with the RAMS model in order to explain the dispersion of HAPs more accurately. However, during the initial time of instantaneous emission, buoyancy term play an important role on the vertical locations of dense particles for near surface atmosphere and around source area, indicating the importance of densities of HAPs in the beginning stage or short duration for the risk assessment of HAPs or management of heavy vapors during the explosive accidents.

• 한국가스학회지
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• 제4권2호
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• pp.7-14
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• 2000

생산지로부터 LNG 선박으로 수송되어 각 생산기지의 저장탱크로 저장되는 액화천연가스 (LNG; Liquified Natural Gas)는 극저은인 Boiling Point보다 약간 낮은 온도 ($-162^{\circ}C$)로 전송된다. LNG 전송은 배관을 통하여 이루어지며, 이로 인하여 배관 내에는 2상 유동 (2-Phase Flow)이 자주 형성된다. 본 연구에서는 일차적으로 이러한 배관내의 2상 유동대한 압력강하량 계산법을 연구하였고, 단열재와 배관 표면을 통한 외부 열유입량과 그에 따른 BOG (Boil-off Gas) 발생량 계산 방법을 연구하여, 이들을 기반으로 LNG 배관시스템의 열유동 해석 프로그램을 개발하였다. 또한 본 연구 및 프로그램 개발을 토대로 최적의 단열재 두께와 배관 Size를 구할 수 있는 최적 설계 프로그램을 구축하였다. 이는 배관설계 시 주어진 최대 허용 압력 강하량과 BOG 발생량 등의 허용 운전 조건과, 단위 길이 당 배관가격과 단위 부피당 단열재가격을 기준으로 허용 범위 내의 최소 설비 비용을 찾는 최적 설계 방법이다.

• 대한핵의학회지
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• 제26권1호
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• pp.133-139
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• 1992

To improve the quality of $^{99m}Tc-methylenediphonate$ $(^{99m}Tc-MDP)$ for skeletal imaging, different composed $^{99m}Tc-MDP$ complexes were prepared with addition of antioxidants such as ascorbic acid, getisic acid, and p-aminobenzoic acid. To characterize the different $^{99m}Tc-MDP$ preparations, some physical and biochemical properties of $^{99m}Tc-MDP$ such as thermal stability, lipophilicity and bindability to serum protein were studied and organ distribution pattern of these complexes also compared. The thermal stabilities of $^{99m}Tc-MDP$ contained antioxidants were dependant mainly on pH, temperature, and elapsed time after the preparation. $^{99m}Tc-MDP$ complex contained gentisic acid as antioxidant was extremely unstable at alkaline condition. The most stable $^{99m}Tc-MDP$ was found in the presence of p-aminobenzoic acid. $^{99m}Tc-MDP$ complexes with antioxidants were very lipophilic but lipophilicity differences in antioxidants were not observed. The bindability of $^{99m}Tc-MDP$ to serum protein was not affect at pH $5.0\sim9.0$ by the different antioxidants. However, protein binding percentage of $^{99m}Tc-MDP$ with ascorbic acid was relatively low (22.7%) at pH 9.0. In biodistribution studies in mice, bone to muscle ratios of $^{99m}Tc-MDP$ preparations containing ascorbic acid, gentisic acid, and p-aminobenzoic acid were 15.3, 24.5, and 30.1, respectively. Im to our results, p-aminobenzoic acid is fond to be the most promising antioxidant.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.515-518
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• 2007

Gas hydrates are ice-like crystalline compounds that form under low temperature and elevated pressure conditions. Recently, gas hydrates present a novel means for natural gas storage and transportation with potential applications in a wide variety of areas. An important property of hydrates that makes them attractive for use in gas storage and transportation is their very high gas-to-sol id ratio. In addition to the high gas content, gas hydrates are remarkably stable. The main barrier to development of gas hydrate technology is the lack of an effective mass production method of gas hydrate in solid form. In this study, some performance comparison among several cases classified by different volume sizes of solution were carried to identify the characteristics due to the volume increment. And it is found that one of the main reasons disturbing hydrate formation is related to the lack of cooling heat transfer due to the volume increase of the solution. So, three kinds of heat transfer plates which have different shapes and cross sectional areas were made and tested for the performance comparison following to the shape and area of each plate. Finally it is clarified that the heat transfer is one of the major factors effecting hydrate formation performance and the installation of heat transfer plate can enhance the formation performance especially not in terms of the quantity but the speed.